1. 1
   A student is studying how the kidney nephron produces urine. Blood enters the kidney and passes through a knot of capillaries called the glomerulus. Here, high pressure forces small molecules out of the blood and into a cup-shaped structure at the start of the nephron tubule, a process called filtration. Blood cells and large protein molecules are too big to be filtered out and remain in the blood. As the filtrate flows along the tubule, useful substances are reabsorbed back into the surrounding blood capillaries.

   (a)

   Which substance passes into the filtrate at the start of the nephron but is normally completely absent from the urine of a healthy person?

   [1 mark]

   • AUrea
   • BGlucose
   • CWater
   • DMineral ions

   (b)

   Which process is responsible for useful substances such as glucose moving back from the kidney tubule into the surrounding blood?

   [1 mark]

   • AFiltration
   • BEgestion
   • CSelective reabsorption
   • DDeamination

   (c)

   Explain why urea is present in the urine of a healthy person but glucose is not.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A runner completes a long race on a hot day and sweats heavily, losing a large volume of water from her body. As a result, her blood plasma becomes more concentrated than normal. Sensors detect this change and trigger a hormonal response that adjusts how much water her kidneys reabsorb, helping to restore the water content of her blood back towards normal.

   (a)

   Which gland releases ADH into the blood when it detects that the blood is too concentrated?

   [1 mark]

   • APancreas
   • BAdrenal gland
   • CThyroid gland
   • DPituitary gland

   (b)

   Immediately after the runner finishes the race, while her blood is still concentrated, what would you expect to happen to the volume and concentration of the urine she produces?

   [1 mark]

   • ASmall volume of concentrated urine
   • BLarge volume of dilute urine
   • CLarge volume of concentrated urine
   • DNo change to urine volume or concentration

   (c)

   Explain, using the idea of negative feedback, how ADH helps to return the runner's blood to its normal water concentration.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient has kidney failure, meaning his kidneys can no longer filter his blood and remove urea effectively. His doctor discusses two treatment options with him: regular dialysis sessions using a dialysis machine, or a kidney transplant from a matched donor.

   (a)

   Explain how dialysis fluid is used to remove urea from a patient's blood without removing useful substances such as glucose and mineral ions.

   [3 marks]

   (b)

   Evaluate the advantages and disadvantages of dialysis compared with a kidney transplant for this patient.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An athlete follows a high-protein diet to support muscle repair after intense training. Her body cannot store the excess amino acids this diet provides, and she also sweats heavily during each training session, losing water and ions. Her body must continuously process the excess protein and restore its water and ion balance.

   (a)

   Explain how excess amino acids from the athlete's high-protein diet are broken down and safely removed from her body, referring to both the liver and the kidneys.

   [6 marks]

   (b)

   Explain how the athlete's body works to maintain water and ion balance during and after an intense training session in hot conditions.

   [6 marks]

   Total for question 4: 12 marks

End of questions